In a typical integrated circuit, the power supply voltage may exhibit transient variations that adversely affect performance of the IC. Voltage drivers are often used to produce a slightly lower regulated voltage (e.g. Vgg) from a higher supply voltage (e.g. VccAux). A typical IC may include many voltage drivers distributed in different regions of the IC for power regulation. Due to variations in impedance, transmission lines of varying lengths, and variation in transistor performance across an integrated circuit (IC), it can be difficult to provide a regulated voltage that is uniform across the IC.
In some previous systems, the driver circuits were controlled by a single regulation circuit. The regulation circuit compared the regulated output voltage, Vgg, to a reference voltage, Vgg_ref, to produce a gating voltage that indicates any difference between Vgg and Vgg_ref. For example, if Vgg dropped below the expected Vgg_ref, the gating voltage from the regulation circuit would increase. When the gating voltage increased above a threshold, it caused the driver circuits to pass current from VccAux to the Vgg output. The current passing to the Vgg output causes the regulated Vgg output voltage to increase and the gating voltage to decrease.
However, this method does not provide stable regulation in larger area ICs. Due to variations in impedance and resistance across the IC and distribution over transmission lines of varying lengths, the gating voltage was not consistent across the IC. As a result, the regulated Vgg output from the voltage drivers may vary geographically as the area of the IC is increased.
To mitigate these affects, some systems include intermediate unity buffers between the regulation and driver circuits to distribute the gating voltage over a wider area. When implemented in an IC with larger areas, intermediate unity analog buffers are included between the regulation and driver circuits to drive signals to their destination driver circuits. However, the unity buffers introduce additional error due to variation of transistors in different buffer circuits. These variations reduce system stability of the IC.
The value of the phase margin is another characteristic of voltage supply circuits that is affected by process variations. Voltage supply circuits, which regulate Vgg using a feedback loop comparison, are subject to oscillations under certain conditions. In adverse conditions (e.g., in high temperatures, or in an integrated circuit manufactured at the fast process corner) such a loop can begin to oscillate. If the phase margin of the circuit is sufficiently large, the oscillation will abate. If the phase margin of the circuit is too small, the response time of one or more driver circuits may be too great, resulting in an overcorrection. As the circuit repeatedly overcorrects for the error, the Vgg voltage will oscillate up and down and the integrated circuit will not function properly.
One or more embodiments of the present invention may address one or more of the above issues.